1. Field of the Invention
The present invention relates to a light guide plate for a surface light-emitting device and a method of manufacturing the same, and more particularly, to a light guide plate for a surface light-emitting device and a method of manufacturing the same, wherein the light guide plate is constructed in the form of an optical waveguide including an upper cladding film, core films formed with V-cut grooves, and a lower cladding film, so that, since the upper and lower cladding films with a relatively low refractive index are respectively located on upper and lower surfaces of the core films, external foreign substances cannot penetrate into the core films to prevent from being brought into contact with other components, whereby optical transmission properties are not changed to thereby enhance the brightness.
2. Description of the Related Art
A liquid crystal display is basically constituted of a liquid crystal display panel and a backlight unit disposed at the rear of the panel.
The liquid crystal display panel serves to display an image by controlling transmitted light, and the backlight unit functions to supply the liquid crystal display panel with light.
In a backlight unit employing the lateral illumination, a light source is disposed at the side of the liquid crystal display to make the liquid crystal display device thin.
FIG. 1 is a side view schematically illustrating the structure of a general liquid crystal display. As shown in the figure, a light guide plate (11), a diffusion plate (12), a prism sheet (13) and a liquid crystal display panel (14) are sequentially disposed on a reflection plate (10). At the side of the light guide plate (11) is disposed a fluorescent lamp (15). Light exiting from the fluorescent lamp (15) is incident on the side of the light guide plate (11). The backlight unit including the reflection plate (10), the light guide plate (11), the diffusion plate (12), the prism sheet (13), and the like converts incident linear light into surface light, and allows the converted surface light to be incident on the liquid crystal display panel (14).
Functions of the respective components of the backlight unit will now be described in more detail. First, the light guide plate (11) serves to allow light from the fluorescent lamp (15) to be incident therein and then uniform surface light to be outputted on the entire upper surface.
The reflection plate (14) disposed at the rear end of the light guide plate (11) allows light from the fluorescent lamp (15) to be incident on the light guide plate (11), and the diffusion plate (12) is disposed on the light guide plate (11) to obtain uniform brightness according to a viewing angle.
Further, the prism sheet (13) serves to increase front-side brightness of light, which is transmitted and radiated upwardly from the diffusion plate (12). The prism sheet (13) allows only light with a predetermined incident angle to pass therethrough and light with the other incident angles to be totally reflected and thus returned to a lower side of the prism sheet (13). In such a case, the returned light is again reflected by the reflection plate (10) attached below the light guide plate (11).
As described above, one of the most important technical features in the field of a liquid crystal display panel is design and manufacturing technologies of a light guide plate that laterally converts incident linear light into surface light and then outputs the surface light uniformly throughout the entire surface.
FIG. 2 is a schematic cross-sectional view of a light guide plate in a surface light-emitting device according to the prior art. A surface light-emitting device such as a liquid crystal display includes a light guide plate (11), as shown in FIG. 1. Dot patterns (11a) are formed on a bottom surface of the light guide plate (11).
Light incident on the side of the light guide plate (11) is reflected on an interface of the light guide plate (11), also reflected on the dot patterns (11a) and then incident on a liquid crystal display panel.
Such a light guide plate using dot patterns is unable to diffuse light only upward. A beam pattern of light outputted from the light guide plate (11) with the dot patterns (11a) provided thereon has a spherical beam pattern (50), i.e. a beam pattern of Lambertian distribution, as shown in FIG. 3. Thus, use of a prism sheet is a must for enhancing the front brightness.
Meanwhile, a mere 50% of light outputted from the fluorescent lamp is transmitted to the liquid crystal display panel while passing through the light guide plate, the diffusion plate and the prism sheet, which results from coupling and absorption losses in the light guide plate, loss in the reflection plate, absorption and surface reflection loss in the diffusion plate, and surface reflection loss in the prism sheet.
Accordingly, as the number of components defining the backlight unit is reduced, the optical loss can be reduced enabling an overall cost reduction. There is another problem in that since an additional process of forming the dot patterns (11a) on the bottom surface of the light guide plate (11) is required in the conventional light guide plate (11), the productivity is reduced. There is a still another problem in that occurrence of defective dot patterns can reduce the yield.